updated xorg conf with composites added:

Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0"
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
EndSection

Section "Files"
    FontPath        "/usr/share/fonts/misc/"
    FontPath        "/usr/share/fonts/Type1/"
    FontPath        "/usr/share/fonts/100dpi/"
    FontPath        "/usr/share/fonts/75dpi/"
    RgbPath         "/usr/lib64/X11/rgb"
EndSection

Section "Module"
    Load           "dbe"
    Load           "extmod"
    Load           "type1"
    Load           "freetype"
    Load           "glx"
EndSection

Section "InputDevice"
    Identifier     "Keyboard0"
    Driver         "kbd"
    Option         "AutoRepeat" "500 30"
    Option         "XkbRules" "xorg"
    Option         "XkbModel" "pc101"
    Option         "XkbLayout" "us"
EndSection

Section "InputDevice"
    Identifier     "Mouse0"
    Driver         "mouse"
    Option         "Protocol" "Auto"    # Auto detect
    Option         "Device" "/dev/input/mice"
    Option         "ZAxisMapping" "4 5 6 7"
    Option         "Emulate3Buttons"
EndSection

Section "Monitor"
    Identifier     "Monitor0"
    VendorName     "SONY"
    ModelName      "Sony GDM-FW900"
    HorizSync       30.0 - 121.0
    VertRefresh     48.0 - 160.0
EndSection

Section "Monitor"
    Identifier     "Monitor1"
    VendorName     "SGI"
    ModelName      "SGI 1600sw"
    HorizSync       31.5 - 121.0
    VertRefresh     60.0 - 150.0
EndSection

Section "Device"
    Identifier     "Videocard0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce 8600 GTS"
    BusID          "PCI:1:0:0"
    Screen          0
#    Option        "AllowGLXWithComposite" "false"
#    Option         "RenderAccel"          "true"
#    Option         "backingstore"         "true"
EndSection

Section "Device"
    Identifier     "Videocard1"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce 8600 GTS"
    BusID          "PCI:1:0:0"
    Screen          1
#    Option         "AllowGLXWithComposite" "false"
#    Option         "RenderAccel"           "true"
#    Option         "backingstore"          "true"
EndSection

Section "Screen"
    Identifier     "Screen 1"
    Device         "Videocard1"
    Monitor        "Monitor1"
    DefaultDepth    24
    SubSection     "Display"
        Depth       24
        Modes      "1600x1024"
    EndSubSection
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Videocard0"
    Monitor        "Monitor0"
    DefaultDepth    24
    SubSection     "Display"
        Viewport    0 0
        Depth       24
        Modes      "1920x1200"
    EndSubSection
EndSection

Section "Extensions"
    Option "Composite" "Enable"
EndSection